Perforated weir in flash distillation

ABSTRACT

A flash evaporator having a plurality of adjacent rectangular flash chambers defined by partition walls and arranged in a straight line horizontally, each of said rectangular flash chambers being provided with flash means comprising an orifice provided at the lower part of each of said partition walls for introducing brine thereinto, a weir having at least one hole therein and being set a proper distance apart from each of said partition walls, and a baffle-board provided so as to cover said weir at a proper distance therefrom, whereby the brine is effectively evaporated in the flash chamber by being fully mixed and agitated by said flash means.

United States Patent Yoshito Kawaguchi;

[72] Inventors Kenkichi Izumi, both of Hitachi-shi, Japan [21] Appl. No. 845,788 [22] Filed July 29, 1969 [45] Patented Dec. 28, 1971 [73] Assignee Hitachi, Ltd.

Tokyo, Japan [32] Priority July 29, 1968 [33] Japan [31] 43/52965 [5 4] PERFORATED WEIR IN FLASH DISTILLATION 1 1 Claims, 6 Drawing Figs.

[52] US. Cl 202/173, 159/2 MS, 203/11, 203/88 [51] Int. Cl 801d 3/06 [50] Field of Search 203/10, 1 1, 88; 202/172, 173, 174, 235, 236; 159/2 MS [56] References Cited UNITED STATES PATENTS 3,192,132 6/1965 Loebel 202/173 Primary Examiner-Norman Yudkoff Assistant ExaminerDavid Edwards Attorney-Craig, Antonelli & Hill ABSTRACT: A flash evaporator having a plurality of adjacent rectangular flash chambers defined by partition walls and arranged in a straight line horizontally, each of said rectangular flash chambers being provided with flash means comprising an orifice provided at the lower part of each of said partition walls for introducing brine thereinto, a weir having at least one hole therein and being set a proper distance apart from each of said partition walls, and a baffle-board provided so as to cover said weir at a proper distance therefrom, whereby the brine is effectively evaporated in the flash chamber by being fully mixed and agitated by said flash means.

PATENTED BEC28 I97! sum 1 or 2 FIG. 2

FIG. 3

o o ja o o ogo 27b 270 1 INVENTORS ATTORNEY5 PERFORATED WEIR IN FLASH DISTILLATION BACKGROUND OF THE INVENTION This invention relates to flash evaporators.

In multistage flash-type evaporators, it is usual to provide series of flash chambers wherein a part of the heated liquid is evaporated successively. The heated liquid is passed successively from a flash chamber under high pressure to a flash chamber under low pressure through orifices communicating with the lower parts of the flash chambers which are arranged vertically side by side. The vapor moves upwards and it transmitted to a condenser through an outlet located in the upper part of each flash chamber. Brine in each of the flash chambers heated to a higher temperature than the saturation temperature according to the pressure of the flash chamber is jetted through the orifice into an adjacent flash chamber. Remaining brine which is not evaporated in the previous flash chamber which is under the higher pressure is also jetted through the orifice into the following flash chamber which is under the lower pressure than said previous flash chamber.

In case, for exhaustively converting the latent heat of the brine jetted through the orifice into the evaporation energy, the brine must be agitated sufficiently through the orifice, it is necessary to contact as desirable a condition as possible with the space of each of the flash chambers in which brine is jetted and it is necessary that the vapor generated by means of the jetting operation be separated sufficiently from the remaining brine. Accordingly, the orifice must be constituted so as to effect the foregoing evaporation operation, to keep the water level of brine in the flash chambers at a predetermined height and to prevent the leakage of the vapor away from the previous flash chamber into the following flash chamber. As described in the foregoing, an excellent orifice is needed so that the orifice is one of the most important elements of the flash evaporator. Thus, the capability of the evaporator is greatly effected by the structure of the orifice.

OBJECTS OF THE INVENTION The first object of this invention is to provide a novel flash evaporator having excellent flash action. Other objects and advantages will be apparent to those skilled in the art from the following detailed description when considered with the accompanying drawings.

SUMMARY OF THE INVENTION According to the invention, a flash evaporator comprises a fluid-evaporating casing, a plurality a flash chambers defined by a plurality of partition walls provided in said fluid-evaporating casing, a condenser provided in each of said flash chambers and flash means providing at least one orifice at the lower part of each of said partition walls, a weir provided in each of said flash chambers being spaced by a predetermined distance from each of said partition walls, said weir being provided with at least one hole on its upper portion and a baffle-board covering said weir by a predetermined distance.

The invention will be more fully described when considered with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view of flash means embodying this invention;

FIG. 2 is a vertical sectional view of a flash evaporator being provided with the flash means shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along the line Ill-III of FIG. 1;

FIG. 4, 5 and 6 are side sectional views of other embodiments of flash means embodying this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 shows a multistage flash evaporator, more particularly a sixflash chamber-type flash evaporator, in each chamber of which is provided the flash means in accordance with the invention, as illustrated in FIG. 1. Referring first to LII FIGS. 2 and 3, a common rectangular casing l is formed by a pair of flat sidewalls 2 and 3, upper and lower walls 4 and 5, and a pair of flat end walls 6 and 7. Flat generally rectangular partition walls 8, 9, l0, l1 and 12 in said casing divide said easing into six adjacent rectangular flash chambers I3, 14, IS, l6, l7 and 18 arranged in a straight line horizontally. Condensing chambers 19, 20, 21, 22, 23 and 24 are respectively provided in said flash chambers in a straight line horizontally and vertically. Flash means 25, 26, 27, 28, 29 and 30 for promoting evaporation of brine by means of jetting operation are respectively provided at the hot bring introducing portions of the flash chambers. Each of said flash means includes each of said partition walls as its own portion.

Features of the flash means embodying this invention are more fully described in accordance with the embodiment shown in FIG. I. Said flash means comprises at least one orifice 251 at the lower part of each of said partition walls, a weir 26 provided in each of said flash chambers and spaced a predetermined distance from each of said partition walls, said weir having a plurality of holes 27a, 27b ..on its upper portion, and a baffle-board 28' covering said weir for a predetermined distance so as to form a passage 29'. Hot brine introduced from a hot brine inlet 31 into the flash chamber 13 flows into the flash means and abruptly flashes out and evaporates a part of itself in accordance with the pressure disparity between the inlet side and the flash chamber 13. Remaining brine in the flash chamber 13 flows through an orifice 251 into the adjacent or following flash chamber 14 due to the pressure disparity between each of said flash chambers, as described in the foregoing. Mixed flow of two phases, that is, the flashed vapor and brine is further expanded and agitation and mixture of said mixed flow is fully promoted when said mixed flow is moving upwards into passage 32 defined by the flat generally rectangular partition wall 8 and the weir 26. A portion of mixed flow of two phases, that is, the vapor and brine expanded in the passage 32, passes through the holes in weir 26 and jets into the passage 29' defined by the weir 26 and the baffle-board 28'. The main portion of said mixed flow which raised along the weir 26 in the passage 32 is deflected from its own flow direction by means of the baffle-board 28' and goes down along the baffle-board 28 in the passage 29. The edge of said baffle-board is extended downwards to about a half the height of the weir 26 and the divergent passage 29 is defined between said weir and said baffle-board. One of the features achieved by the flash means employed by this invention is to provide good conditions of flow which make it possible to obtain perfect flashing of brine in the passage 29 of said flash means. Said flash means acts to agitate the brine sufficiently in the passage 29' in such manner that the main portion of mixed flow of two phases which flowed downwards while expanding in said divergent passage collides with a diverged portion of said mixed flow jetted through the holes 27a, 27b ..into said passage and latent heat held in the brine is converted to evaporation energy exhaustively.

If brine which flows out through the flash means produces additional flashing in the flash chamber 14, small drops of brine scattered by said additional flashing are transferred with the vapor into the condenser 20 or they scatter directly into the above-mentioned condenser. With this poor operation of the flash evaporator, it will be difficult to produce high purified fresh water. According to this invention, brine is mixed and agitated sufficiently in the passage 29' of the flash means and latent heat being held in said brine is converted to evaporation energy exhaustively so that the above-mentioned additional flashing in the next adjacent flash chamber is effectively prevented which makes it possible to produce remarkably more highly purified fresh water.

As the flash means is comprised in such construction that mixed flow of two phases, that is, vapor and brine is forced to flow downwards through the passage 29' defined by the baffleboard 28' and the weir 26, brine which is not still evaporated falls downwards through the passage 29' and the vapor rises up to the condenser 20 by changing its own flowing direction upwards after it once flows downwards along the baffle-board 28', so that separation of the vapor and brine is sufficiently achieved and highly purified fresh water is produced.

As shown in FIG. 1, another baffle-board 33 is provided as an extension at the tip of the baffle-board 28' generally extending horizontally. In such a case, a portion of brine which flows out and falls downward through the passage 29 collides with the liquid surface of brine staying on the downward part of the flash chamber 14 and small drops of brine are scattered upwards from the liquid surface. Highly purified fresh water is produced by means of gathering the small drops of brine from the liquid surface.

Another feature according to this invention is the novel action caused by the holes 27a, 27b ..provided on the weir 26. As at the starting up period of the flash evaporator, even when a pressure disparity between each of flash chambers is smaller than a predetermined pressure disparity, effective operation of the flash evaporator can be achieved by the weirs employed in this invention. In such flash means as shown in FIG. 1, the action force for producing flow of brine from the flash chamber 13 into the flash chamber 14 is explained by the equation:

In the above equation, P, a and P, represent a pressure in the flash chamber 13 and a pressure in the flash chamber 14, respectively, h, represents the depth from the lower wall 5 of the common rectangular casing l to the liquid surface of the brine, 7 represents the specific gravity of the brine, 'y,, represents the average specific gravity of the mixed flow of two phases in the passage 32, h, represents a height of weir 26 from the lower wall 5 of the common rectangular casing l, h, represents the pressure-loss of the liquid which passes through the orifice 251, the passage 32 and the passage 29. The left side of the above equation represents the total pressure disparity for brine flowing from the flash chamber 13 into the flash chamber 14. Brine scarcely flashes in each of the flash means if said pressure disparity between each of the flash chambers is smaller than the predetermined pressure disparity at the starting up period. Accordingly h the second term in the right side of the above formula, is nearly equal to zero and 7, the first term in the same side of the above formula, is also equal to the specific gravity 7 of the brine. In other words, brine begins to flow through both of the flash chambers when the total pressure disparity between the adjacent flash chambers has fully become sufficient to lift up brine to a top edge of the weir. In an excellent flash evaporator, it is necessary to achieve such contradictory demands that the height of the weir, that is, the flash means, is to be constructed as much lower as possible if the operator desires to operate the flash evaporator when the pressure disparity between each of the adjacent flash chambers is small and on the other when the liquid surface of the height of the weir is needed to be constructed as much higher as possible if the operator desires to operate the flash evaporator without having the flash means extend into the brine when the liquid surface of the brine in the flash chambers is changed up and down. The flash means employed by this invention can satisfy the above two demands which appear contradictory at first sight.

Especially in such case where the brine scarcely flashes because the pressure disparity between the adjacent flash chambers is small at the starting up period, all of the brine rising along the weir 26 in the passage 32 passes through the holes 27a, 27b ..provided at said weir into the next flash chamber so that said holes provide substantially the same effect as ifthe height of said weir were made lower. On the other I hand, in the case where said pressure disparity is sufficiently large, a main portion of the mixtured flow of two phases, that is, brine which flashed in the aperture 32 and the vapor, flow over the weir 26 into the passage 29' and another portion of said mixtured flow passes through said holes so that the height of said weir has become higher than that of the foregoing condition. Size, numbers and position of the holes 27a, 27b ..which are to be provided at the weir 26 are determined to suit the operating condition and are considered as the vapor in each of the flash chambers does not pass through said holes into each ofthe adjacent flash chambers.

FIG. 4 shows another embodiment of flash means in accordance with the invention having an inclined orifice at the lower part of partition wall 81, as shown by numeral 34. The inclined angle is provided so as to flow partially a two phaseflow passing in a passage 321 defined by the partition wall 81 and a weir 261 and to regulate said flow into a uniform flow so that the amount of separated flow is controlled.

FIG. 5 shows another embodiment of flash means having holes 271a, 27lb ..provided with nozzle-type guides 35a, 35b A minor portion of mixtured flow of the two phases jetted through the holes 271a, 27lb ..is regulated horizontally by means of said nozzle-type guides and collides forcefully with a major portion of said mixtured flow flowing downwards in passage 292 so that both of said flows are mixed and agitated excellently with each other.

FIG. 6 shows still another embodiment of flash means having a plurality of baffle-plates 36a, 36b, 36c ..extending from a baffle-board 333 in addition to the construction shown in FIG. 1. According to this construction, agitation of the mixtured flow of two phases in the passage 293 is further promoted.

Although we have consistently described the use of the partition wall which defines the fluid-evaporating casing as one of elements for constituting the flash means, as is well known, there is no partition wall at the inlet portion of the primary flash chamber of the flash evaporator. In such case, the flat end wall 6 of the casing is utilized instead of said partition wall as shown in FIG. 2. Though we have explained that each of the weirs is provided in a parallel manner with each of partition walls in the embodiments shown in FIG. 1 to 6, said weir may be provided to have a desirable inclined angle to said partition wall. Since many modifications and variations may be made in the described flash evaporator without departing from the spirit of the invention, the foregoing description is to be considered as exemplary and not in a limiting sense. It is therefore to be understood that many changes may be made in the par ticular embodiment disclosed which are within the full intended scope of the invention.

We claim:

1. A flash evaporator comprising an enclosed fluid-evaporating casing having a plurality of partition walls defining a plurality of adjacent flash chambers,

a condenser provided in each of said flash chambers, and

flash means including at least one orifice in the lower part of each of said partition walls interconnecting adjacent flash chambers, a weir provided in each of said flash chambers and being spaced a predetermined distance from one of said partition walls, said weir being provided with at least one hole in its upper portion where fluid to be evaporated is agitated in such a manner that said fluid flowing over said weir collides with flowjetted through said hole, and a baffle-board extending from said one partition wall over said weir a predetermined distance to form a passage therebetween.

2. A flash evaporator as defined in claim I, wherein said weir is positioned adjacent said one partition wall at the inlet side of said flash chamber to form an inlet passage with said one partition wall.

3. A flash evaporator as defined in claim 2, wherein said inlet passage and said passage between said weir and said baffle-board communicate above the top of said weir.

4. A flash evaporator as defined in claim 3, wherein said weir has a plurality of holes therein the upper portion thereof and said baffle-board extends down at least to the lowest level ofsaid holes.

5. A flash evaporator as defined in claim 4, wherein said baffle-board is provided with a substantially horizontally disposed extension from the lower end thereof.

6. A flash evaporator as defined in claim 2, wherein the portion of said bafi'le-board adjacent said weir is angled so that the passage therebetween is divergent.

7. A flash evaporator as defined in claim I, wherein the said lower part of each of said partition walls containing said orifice is inclined to the vertical.

8. A flash evaporator as defined in claim 1, wherein a nozzle-type guide is provided on said weir in association with said hole therein.

9. A flash evaporator as defined in claim 1, wherein said bafi'leboard is provided with at least one baffle plate extending therefrom in said passage toward said weir.

10. A flash evaporator for effecting evaporation of water from brine in successive chambers of progressively decreasing pressure comprising an enclosed fluid evaporating casing having a plurality of partition walls defining a plurality of adjacent flash chambers, each of said partition walls having an orifice in the lower part thereof for introducing heated brine into an adjacent flash chamber under pressure,

a weir provided in each of said flash chambers and being spaced a predetermined distance from the partition wall at the inlet side of the flash chamber to form an inlet passage, said weir being provided with a plurality of holes in its upper portion where fluid to be evaporated is agitated in such a manner that said fluid flowing over said weir collides with fluid flow jetted through said plurality of holes thereof, and

a baffle-board in each flash chamber extending from the partition wall adjacent said weir around said weir to form a divergent passage therebetween, the height of said weir in a second flash chamber being h =P"P+-yhh/'y"' where P" and P are pressures in first and second adjacent flash chambers, h is the depth of the brine in the first flash chamber, y is the specific gravity of the brine in general, is the specific gravity of the brine in said inlet passage, and h" is the pressure loss of the brine in passing through the orifice to the second flash chamber.

11. A flash evaporator comprising: an enclosed fluid evaporating casing having a plurality of partition walls defining a plurality of adjacent flash chambers, a condenser disposed in each of said flash chambers, and a flash assembly including at least one orifice located in the lower portion of each of said partition walls interconnecting adjacent flash chambers,

a weir disposed in each of said flash chambers and being spaced a predetermined distance from one of said partition walls, so as to define a fluid flow passageway therewith, said weir being provided with means for directing fluid flow transverse to the direction of the flow of fluid which passes over said weir and traverses said passageway, said means including at least one hole in the upper portion of said weir, and a baffle-board extending from said one partition wall over said weir a predetermined distance to form said passageway therebetween. 

2. A flash evaporator as defined in claim 1, wherein said weir is positioned adjacent said one partition wall at the inlet side of said flash chamber to form an inlet passage with said one partition wall.
 3. A flash evaporator as defined in claim 2, wherein said inlet passage and said passage between said weir and said baffle-board communicate above the top of said weir.
 4. A flash evaporator as defined in claim 3, wherein said weir has a plurality of holes therein the upper portion thereof and said baffle-board extends down at least to the lowest level of said holes.
 5. A flash evaporator as defined in claim 4, wherein said baffle-board is provided with a substantially horizontally disposed extension from the lower end thereof.
 6. A flash evaporator as defined in claim 2, wherein the portion of said baffle-board adjacent said weir is angled so that the passage therebetween is divergent.
 7. A flash evaporator as defined in claim 1, wherein the said lower part of each of said partition walls containing said orifice is inclined to the vertical.
 8. A flash evaporator as defined in claim 1, wherein a nozzle-type guide is provided on said weir in association with said hole therein.
 9. A flash evaporator as defined in claim 1, wherein said baffle-board is provided with at least one baffle plate extending therefrom in said passage toward said weir.
 10. A flash evaporator for effecting evaporation of water from brine in successive chambers of progressively decreasing pressure comprising an enclosed fluid evaporating casing having a plurality of partition walls defining a plurality of adjacent flash chambers, each of said partition walls having an orifice in the lower part thereof for introducing heated brine into an adjacent flash chamber under pressure, a weir provided in each of said flash chambers and being spaced a predetermined distance from the partition wall at the inlet side of the flash chamber to form an inlet passage, said weir being provided with a plurality of holes in its upper portion where fluid to be evaporated is agitated in such a manner that said fluid flowing over said weir collides with fluid flow jetted through said plurality of holes thereof, and a baffle-board in each flash chamber extending from the partition wall adjacent said weir around said weir to form a divergent passage therebetween, the height of said weir in a second flash chamber being h7 Pa-Pb+ gamma ha-h0/ gamma m where Pa and Pb are pressures in first and second adjacent flash chambers, ha is the depth of the brine in the first flash chamber, gamma is the specific gravity of the brine in general, m is the specific gravity of the brine in general, gamma mis the specific gravity of the brine in said inlet passage, and ho is the pressure loss of the brine in passing through the orifice to the second flash chamber.
 11. A flash evaporator comprising: an enclosed fluid evaporating casing having a plurality of partition walls defining a plurality of adjacent flash chambers, a condenser disposed in each of said flash chambers, and a flash assembly including at least one orifice located in the lower portion of each of said partition walls interconnecting adjacent flash chambers, a weir disposed in each of said flash chambers and being spaced a predetermined distance from one of said partition walls, so as to define a fluid flow passageway therewith, said weir being provided with means for directing fluid flow transverse to the direction of the flow of fluid which passes over said weir and traverses said passageway, said means including at least one hole in the upper portion of said weir, and a baffle-board extending from said one partition wall over said weir a predetermined distance to form said passageway therebetween. 